Storm index predicts ice damage

Over the past decade Oklahoma's sustained $1.5 billion in damages from eight ice storms, five of which left some areas without power for weeks. In 2007, after back-to-back onslaughts in the three-county Panhandle, the state was ready to fight back.

To do this, Sid Sperry of the Oklahoma Association of Electric Cooperatives and Tulsa National Weather Service Meteorologist Steve Piltz designed the "Sperry-Piltz Ice Accumulation Index.", an algorithm that predicts an oncoming storm's severity three to four days in advance. By forecasting footprint and accumulation, the index enables sand and salt crews, utilities, and emergency preparedness teams to better mobilize resources.

The index consolidates historical information from previous ice storms in the state with data collected by the Oklahoma Mesonet, a network of 120 automated environmental monitoring stations that collects data 24/7 and transits information every five minutes. Each of the state's 77 counties has at least one Mesonet station.

Damage potential is gauged by accumulation, wind speed, and temperatures:

Level 1 - Some isolated or localized utility interruptions are possible, typically lasting only a few hours. Roads and bridges may become slick and hazardous.

Level 5 - Catastrophic damage to entire exposed utility systems, including both distribution and transmission networks. Outages could last several weeks in some areas. Shelters needed.

Level 1 or Level 5?

By combining accumulation, wind speed, and temperatures, the index categorizes utility- and road-related conditions much like the Fujita scale categorizes potential damage from a tornado.

For example, utility systems may be able to handle moderate accumulations, but lines, poles, and other structures are more likely to break when wind speeds increase. Therefore, 1 inch of ice may be a Level 2 or Level 3 ice event, but if winds exceed 25 mph, it becomes a Level 5 event.

In a blog comment earlier this year, Sperry explained how the index came to be: "Steve and his team were eager to help, and within a matter of hours had an algorithm put together using the parameters that I gave them for radial ice accumulation, wind speeds and directions, and temperatures during an icing event."

The index is rapidly growing in popularity among emergency managers and other disaster preparedness agencies.

"We hope it proves to be a useful tool to the citizens of Oklahoma, and to all those who are impacted by ice storm disasters," says Sperry.